Method and apparatus for reducing drag on submerged vehicles



Jan. 29, 1963 H. P. EICHENBERGER 3,075,489

METHOD AND APPARATUS FOR REDUCING DRAG ON SUBMERGED VEHICLES Filed Oct. 28. 1960 5 Sheets-Sheet 1 Jan. 29, 1963 H. P. EICHENBERGER 3,075,489

METHOD AND APPARATUS FOR REDUCING DRAG 0N SUBMERGED VEHICLES Filed on. 28. 1960 3 Sheets-Sheet 2 Jan. 29, 1963 'H. P. EICHEINBERGER METHOD AND APPARATUS FOR REDUCING DRAG ON SUBMERGED VEHICLES Filed Oct. 28. 1960 5 Sheets-Sheet 3 WATER 6/15 I INTER/546E fHKEHfUF Hans fiaenieryer United States grind This invention relates to methods and apparatus for reducing the drag of bodies or vehicles, such as torpedo, submarine and the like submerged and moving in a iquid medium, such as water. More particularly, the present invention relates to improved methods and means for providing a multiiold reduction of such drag-by stabilization of a laminar water boundary layer through employment of a gas film introduced between the body and the surrounding liquid medium whereby stabilization of the laminar water boundary layer also results in stabilization of the gas-water interface.

It is a feature of the present invention to introduce gas onto the surface of a body moving in a liquid medium in such a manner that the velocity of the liquid at the liquid-gas interface is a fraction of the velocity of the body itself.

it is also a feature of the present invention to adjust a gas sheet layer and the flow of liquid around a body which is moving in a liquid medium in such a manner that the interface between the liquid and the gas is stable, i.e., in such a manner that the gas film does not break up into bubbles. The thickness of the gas film layer may be maintained or controlled by continuous injection of gas and removal of a part of the existing gas layer through porous walls or slots formed in the body. Stability of the gas-water interface may also be improved by reduction of shear stress on the gas-water interface. Ap-

paratus for achieving such shear reduction may include the provision of ridges or fins on the major outer surface body for deflecting a portion of the gas film at an angle to the direction of t e velocity of the body in a manner to be described in more detail below.

it is another feature of the present invention to provide means for separating a moving body, such as a torpedo, submarine and the like immersed in a liquid medium from the liquid by a gas film in such a manner as to maintain the stability of a laminar liquid boundary layer and the stability of the interface between the gas and the liquid.

Experience has indicated that a stable interface and boundary layer between a gas film and the ambient liquid medium may reduce drag on the body or vehicle of an order of magnitude of a hundred-fold. Drag reduction results in a concomitant reduction in the propulsive power requirements per unit weight of the vehicle while afiording a multi-fold reduction in the noise transmitted from the body. to the ambient liquid medium. In order to achieve these results, however, it has been found that the mere provision of a gas film per se is insufiicient. it is essential that the gas-liquid interface be maintained in a stable state as more fully hereinafter described, or at least in such a small degree of instability that break up of the interface does not occur prematurely around the vehicle body. it is a still further feature of the present invention to provide an improved exterior configuration for torpedoes, submarines and the like, which facilitate introduction of the gas film around the body or vehicle in such a manner as to substantially increase separation of the body from the surrounding water over the major portion of the body or vehicle.

In this arrangement, the nose or front portion of the atent body or vehicle is partially concave in longitudinal section as seen from the vehicle. The gas film is introduced onto the surface of the body from a location at the front of the body in a layer thickness approximating the layer thickness required to maintain either a laminar 0r turbulent gas layer and stable (or as remarked above slightly unstable) laminar liquid boundary layer (and thus a stable water-gas interface around the remainder of the vehicle body) and where the flow of the water boundary layer formed in front of the body or vehicle is in a transition state from a stagnation condition to an acceleration condition. The particular vehicle or body configuration and the particular area of introduction of the gas film over the outer surface of the vehicle result in a gas film layer at the point of introduction of a thinness minimizing possible stagnation point instability, such as cross-flow, and minimizing the introduction of waves which may lead to the breaking of the water gas interface around the vehicle body.

It is therefore an object of this invention to provide a method and apparatus for reducing the drag of a body or vehicle submerged and moving in a liquid medium.

E is another obiect of the present invention to provide a method and apparatus for reducing drag on a body or vehicle submerged in and moving in a liquid medium by interposing a gas film between the body and the liquid and maintaining the gas film in such a condition as to stabilize a laminar liquid boundary layer and the liquidgas interface.

it is still another object of the present invention to provide a method and apparatus for reducing the drag of a body or vehicle sub-merged and moving in a first fluid of relative high viscosity by interposing between the body and the first fluid a film of a second fluid of relatively lower viscosity in such a manner as to maintain a laminar boundary layer of said first liquid and to prevent the interface between the fluids from breaking up.

lit is a further object of the present invention to provide a method and apparatus for reducing the drag on a submerged body or vehicle moving in a liquid medium wherein the shear stress acting on the interface between the liquid medium and a gas film interposed between the body or vehicle and the liquid medium is reduced to a minimum.

it is a still further object of the present invention to provide a method and apparatus for reducing drag on a body or vehicle submerged and moving in a liquid medium wherein the thickness of a gas film (interposed between the submerged moving body or vehicle and the liquid medium in which the body or vehicle is moving) is maintained at a desired value by introducing such gas through a plurality of openings located adjacent the front of the moving body or vehicle and withdrawing the gas film through another set of openings in the body or vehicle and continuously recirculating the gas.

It is still another object of the present invention to provide a method and apparatus for reducing drag on submerged bodies or vehicles moving in a liquid medium by interposing a gas film between the liquid medium and the body or vehicle adjacent the front of the body or vehicle at a location where the liquid medium flow is in a transition stage from a stagnation condition to an acceleration condition.

These and other objects, features and advantages of the present invention will become more apparent upon a careful consideration of the following detailed description when considered in conjunction with the accompanying drawings illustrating preferred embodiments of the present invention and wherein like reference numerals and characters refer to like and corresponding parts throughout the several views.

On the drawing:

FIGURE 1 is a diagrammatic longitudinal side elevational view of a vehicle constructed in accordance with the present invention.

FIGURE 2 is a front elevational view of the vehicle of FIGURE 1. V 7 FIGURE 3 is an enlarged fragmentary view in partial elevation taken along lines III-III of FIGURE 2.

FIGURE 4 is an enlarged fragmentary view taken along lines IVIV of FIGURE 3.

FIGURE 5 is a top view of the vehicle of FIGURE 1.

FIGURE 6 is a bottom view of the vehicle of FIG- URE 1.

FIGURE 7 is an enlarged fragmentary view in crosssection illustrating the structure of the blowing slots located on the bottom of the torpedo.

FIGURE 8 is afragmentary view in cross-section illustrating. the structure of the" gas deflecting ridges on the surface of the torpedo.

FIGURE 9 is a view in partial section of the embodiment of FIGURE 1;

As shown on the drawing:

Briefly stated, the present invention relates to. improved methods and means for reducing the drag on a body or vehicle submerged and moving in a fluid medium.

For purposes hereof, the term liquid, with respect to the above classification, is to be understood to mean any fluid which is not a gas. Similarly the term liquid and water will be used interchangeably herein, unless other- Wise specified, although, it is, of course, recognized that water is merely one common example of a liquid.

The present invention is concerned primarily with the problems ofdrag in a liquid for the reason that the invention depends primarily on interposing between a moving body and the ambient liquid medium in which the body is moving a gas layer or film of a viscosity considerably lower than that of the ambient medium.

The problems associated with drag in liquid mediums are completely different from those associated with gaseous mediums, where, as in the case of anairplane, the

surrounding medium is itself a gas, the difference in viscosity which can be achieved by introducing another gas as the film are so small as to render the problems involved essentially different in degree rather than different in kind. While the term gas will be used herein to refer to the above noted film which is to be interposed between the body and its medium, it should be realized that, in some applications, the usual meaning'of the word gas, that is, a fluid which is not a liquid is too restrictive, since, for the present purposes, the term should include, and is used to include, any fluid of a substantially lower viscosity than the liquid in which the body is moving.

Maintenance ofthe laminar water boundary layer, in accordance with this invention, results also in maintenance of the Water-gas interface.

The method of the present invention is'more easily applied when the Reynolds number for the body or vehicle is small. In this sense, the Reynolds number for the body may be defined as being equal to the velocity of the body times the length of the body, the product being divided by the kinematic viscosity of the waterxor other fluid medium in which the body. moves. It is thus apparent that the present invention is particularly suitable for applications where the Reynolds number .of the'body is small as compared to the Reynolds number of vehicles such as torpedoes and submarines.

Basically, there are essentially two conditions which must be established to ensure the existence of a, laminar water boundary layer and the water gas interface therewith. t

The first of these conditions is that the streamline forming the interface between the gas and the water must be convex as seen from the gas side in such a manner that the total body force acting on the water is .awayfrom the gas. The body force per unit mass (acceleration) actingpn the water is the vector sum of the centrifugal force per unit mass andgravity. As is well known, centrifugal acceleration is equal to V /R where V represents the water velocity, and R is the radius of curvature of the surface of the body or vehicle.

The second condition for stability of the water bound ary layer and the gas interface therewith is that the water boundary layer be kept sutficiently small so that it will remain laminar. By a small boundary layer is meant one in which the Reynolds number is small. This number is defined, for this purpose, by the formula:

Vd/ N where V is the water velocity,

d is the-displacement thickness of the water boundary layerand N is the kinematic viscosityof the fluid.

This Reynolds number forthe fluid should be of the order of or smaller. This second condition, maintaining a relatively small fluid Reynolds number, may be achieved by providing devices such that the free streamline is in contact with a solid vehicle wall surface for an extremely short distance, only and consequently, almost no boundary layer is formed in the water. Such devices are de scribedin detail hereinafter.

Once, the interface (free streamline) is formed, two major factors tend to cause instability of the water-gas interface and mustbe overcome in practice.

The, first of, these factors relates to the Taylor instability which is exemplified by the instability of a gas layer onthe bottomof a glass of water. This is the phenomenon. observed wherein the gas breaks up into bubbles which, rise to the surface. of the water. Generally, this type of instability occurs whenever the body force acts inthe direction from the denser fluid (water) toward the less dense fluid (gas). This phenomenon is not necessarily present on the top of the torpedo or submarine, provided centrifugal force exceeds gravity.

The second major factor tending towards instability of the water-gas interfacev is of the same nature as the "instability which leads from a laminar water boundary layer to a turbulent layer. It is clearly a function of the waterboundary layer velocity profile and the Reynolds number in the water. The water boundary layer Reynolds number, based, for instance, on the displacement thickness of the water boundary layer, becomes smaller when the shear stress which is exerted on the water by the gas film. is reduced, other factors being equal. On a typical torpedo, a gas film of thickness produces a shear stress on the torpedo which is so small (about .of the sheapstress which would exist in a laminar water boundary layer for the same torpedo without gas film), that the waterboundary layer may not become turbulent, before it reaches the rear end of the torpedo. More particularly, even though the gas-water interface may tend to become unstable, the amplification of the instability Waves is .not sufliciently large, before reaching the rear endof the torpedo, to form water droplets.

For the purposes of the present application air is desig-- nated as the gas medium, and the purpose for injection thereof is to maintain the water boundary layer laminar. In general, to. establish and maintaindrag reduction, the. following conditions must be met:

(41in order to maintain the water boundary layer laminar,

' vehicle into an annular the location or the gas injector means must show a concave curvature of the surface of the vehicle.

(5') The air removed by suction slots in such a manner that the laminar water boundary layer is maintained relatively stable.

It will be appreciated, of course, that many types of construction of apparatus exist suitable for bodies or vehicles, such as torpedoes and submarines which may be employed in order to achieve the basic conditions for laminar fiow discussed above, namely, convex stream lines and minimum shear forces. These constructions will vary, of course, in accordance with the speed and size require nents of the body.

A typical embodiment of a body or vehicle found useful in the parctice of the present invention, illustrated by a torpedo and generally designated by the numeral 8, appears in FF. 1. The torpedo 8, in operation, is submerged in the liquid medium over the entire surface area thereof. The rear end he of the vehicle is shaped in a conventional manner and houses the vehicle propulsion device {not shown) and the front end 8b of the vehicle may comprise a substantially fiat surface in side elevation having a central arcuate dished-in or cup-shaped recess surrounded by an annular outer portion Sl, externally gencrally convex in peripheral section, for purposes hereinafter more fully described.

Water Boundary Layer Removal in order to provide a dra reduction for a vehicle or body moving in a liquid medium, the water boundary layer formed in front of the body by contact with the surface of the torpedo is first removed.

From the axis of symmetry A of the torpedo to the convex areas $1, on the vehicle, the water or liquid medium in which the body is moving is in contact with the front of the body and streams from the axis of symmetry j toward the outer surfaces of the body as clearly appears in HG. 1.

Located in [1 e annular outer portion 31 are a plurality of annular sleeves @344 which may be coaxial as shown for removal or" the water boundary layer formed in front of the vehicle by contact therewith. A plurality of channels Wi-Wd are defined by the sleeves 13 through 14 and including a pair of inner and outer sleeve or support members b and 14a. respectively shown cylindrical in configuration and concentric with the sleeves til-lid. The channels disclosed herein, depending upon the configuration of the vehicle with which they are associated, may also be located further back on the body of the vehicle, such as at locations shown in my US. Patent No. 3,816,- 865. such a case, the channels would be axially dis placed. The sleeves therefore would have a suitable configuration as the free water streamline deviates from the radial direction toward the axial direction of the vehicle. Spacers l5 and support members 16 may also be provided for the sleeves 1644. The ambient water boundary layer formed by contact with the front of the ehicle is drawn incrementally into the channels v l-Wb and pump means (not shown) may be provided to assist in this purpose, such as also taught in my US. Patent No. 3,016,865. The boundary layer increments of water are then discharged from each of the sleeves 19-14 in the channel 21 which may discharge through a plurality of ports 2; for purposes of illustration, only one such port is shown, formed in the sleeve support 14b for purposes hereinafter described (PEG. 9). in order to reduce the thiclmess or" the boundary layer on the surface of the torpedo, it is preferable to form the torpedo nose so that the water boundary layer remains laminar in its travel around the torpedo. However, this is not a necessary condition for the functioning of the device of this invention shown in the drawing.

The final water channel W6 draws oh the last more rnent of the boundary layer of water in such a manner that a stagnation point P (HG. 3) is formed on the for ward surface of the knife edge of the outer sleeve 14a. Along the forward surface of the knife edge of the outer sleeve 14a, the water accelerates rapidly from the stagnation point P to the edge or lip l of the knife edge of sleeve Ma where the water forms a free streamline. Because of the extremely small distance from the point P to the lip l and the relatively low average velocity (the velocity is high only over the very last part of this lip near the top of the knife edge) the boundary layer formed in the layer at l is so small that stability is assured.

The water boundary layer thus is removed not by a single channel, but by the multi-channel construction shown. Two major advantages accrue from the multichannel construction. First, instability in the region of water removal which may lead to vibrations are prevented. in particular, the high stagnation pressure streamline which is located at the outside of the water boundary layer and indicated by the letter M (FIG. 3) is prevented frorn curling up and flowing upstream in a region of low stagnation pressure which exists within the water boundary layer near the surface of the torpedo. in addition, the distance over which the streamline forming the water gas interface f flows over the solid surface of the vehicle is increasing with increasing width and with a decreasing suction flow rate to free stream velocity ratio. in order to maintain the latter ratio reasonably small, the width of the channels Vii-W6 must be small.

Gas Film Introduction With the water boundary layer withdrawn through the channels W1-W6, introduction of a gas film at the front end of the body results in reduction of the skin friction of the water against the body over the greatest total area thereof. Consequently, a gas film may be introduced preferably through a plurality of radial channels 34 extending annularly around the convex portion 81 of the vehicle.

This gas film is intended to separate the body or vehicle from the surrounding water over the major portion of the remainder of the length thereof.

At the region where the water boundary layer is removed and where the gas is to be introduced, the surface of the underwater body has a sharp contour, i.e., the tangent to the surface of the torpedo immediately before the introduction of the gas to the surface of the body and the tangent to the body immediately after the introduction of the gas forms a finite angle. This construction permits the water, as seen quantitatively in about a twenty times size detail in FIG. 3, to accelerate suddenly from a region before the point of gas introduction to the region immediately at or after the gas introduction. Additionally, this particular construction results in a gas film which is at the region of gas introduct on almost immediately of a cross-sectional thickness as required for the whole body. Without this sharp contour the gas film thickness in the region of gas introduction would be considerably larger with its inherent disadvantage of cross-flow. Experience has indicated that cross-ilow increases rapidly as the gas film thickness increases.

The possibility of undesirable gas cross-flow is minimized by the provision of a plurality of closely spaced radial partition walls 34a providing thereby a multi-gas flow channel construction (FIGS. 2 and 4).

The gas, supplied through the plurality of radial channels 34-, is in such a quantity that the free streamline, f has a concave curvature as seen from the gas side of the water-gas interface. The location of the sleeve is; and the quantity of the flow of gas, as well as the quantity of water removed through the channels Wl-W, should be adjusted so that the streamline f follows essentially a predetermined streamline which is considered the 6X- terior shape of the torpedo while the gas may be considered a part of the torpedo for these purposes. These conditions then may be adjusted by adjusting the point or lip of the sleeve lda radially outward toward the consmas es tinuation ofthe surface of the frontal nose portion substantially to the position indicated in FIGS. 2 and 3, i.e., so that the l of the sleeve 14a is slightly inside of the continuation of the surface of the frontal nose portion. Adjustment of the projection of the sleeve knife edge may be achieved by the originally fixed dimensioning of the knife edge or otherwise.

The gas is supplied to the channels 34 from a source 23 through a conduit 24 under the influence of a pump 25. Valve means 26 are positioned in conduit 24 and may be operatively responsive to conventional control means 27 which may also control operation of the pump From the valve means 26, the gas is supplied under pressure through a conduit 28 to a manifold 29 which feeds a plurality of supply conduits 30, each of which is interconnected with one of a plurality of plenum chambers 31. Each of the plenum chambers 31 communicates with a number of the gas flow channels 34 .througha plurality of gas metering orifices 32 formed in the outer annular sleeve or support member 14a. The closely spaced radial partition Walls 34a, of the gas channels 34, are provided not only to prevent possible cross-flow in the region of gas introduction to the surface of the torpedo, but also to ensure that the flow rate of gas in each of the channels 34 is the same regardless of the variations in hydrostatic pressure at the outlet of each of the channels 34-. Thus, the same approximate flow rate is imparted to each of the channels through the metering orifices 32.

The flow of water over a gas cavity 34 has a tendency to excite vibrations in the cavitywhich would affect break-up of the water-gas interface. In order to dampen these vibrations, the individual gas channels 34 are thus designed, and the gas flow rate so metered, that the flow in these gas channels is substantially laminar. Laminar flow then has a dampening effect on potential cavity vibration caused by flow of water thereover.

After removal of the water boundary layer, and introduction of the gas'film around the body, the streamline which forms the interface between the water andgas film must be prevented from contacting the body over as great a distance as possible, as by gas replenishment means. I

Gas Replenishment After the gas film has been introduced at the region S1, it may be desirable to replenish the film with additional gas from a source such as slots S2 generally disposed on the bottom of the under Water body as seen by way of example in FIGS. 1 and 6. The slots S2 may be arranged in various patterns and should have special geometric form (shown in detail in cross-section in FIG. 7 and to be described below) such that the slots replenish the gas film thickness but provide a minimum of disturbance to the film. For instance, for a torpedo, the flow in these slots ,must also remain laminar and therefore should be of a very low Reynolds number based on the width W (FIG. 7) of the ,slot such that the gas flow of height h which separates the water from the under water body, is not disturbed. In particular, disturbance may lead to waver in the water and must be avoided. This may, for instance, be achieved by the combination of the following factors as illustrated in FIG. 7. The slot width W may be such that the Reynolds number based on this slot width is no greater than 100 but is preferably near 10. The. left hand corner D of the slot is preferably overhanging and in any event is at least asharp corner. The surface wall 8d to the right (downstream in the gas flow) is slightly depressed and the corner 8e of slot S2 leading to this surface generouslyrounded as shown in FIG. 7.

Gas Removal 'The under water body 8 may alsorbe provided with suction slots S3 on its top surface as shown in FIGS. 1 and 5. The suction slots S3 remove gas from thefilm and'aredistributed in such a manner as to' maintain the 8 gas film thickness within specified limits. For instance, for a torpedo operating at normal speeds, the gas film heightshould be of an order of foot.

In the region of vehicle length where the water flow introduces a positive pressure gradient along the surface of the torpedo, i.e., further back on the torpedo, more gas should be removed on the top surface from the gas film than is introduced on the bottom surface of the vehicle through the 'slots S2. For this purpose, additional suction removal slots S3 may be provided and positioned to run perpendicular to the axis of. the torpedo as shown in FIGS. 1, 5 and 6.

However, the direction of these slots may vary from that shown provided they fulfill the function of keeping :the gas film thickness at its predetermined value. These slots S3 extend more toward the bottom of the torpedo progressively until adjacent the end of the torpedo, gas is also removed at the bottom thereof because the slots are formed to extend in annular fashion completely :around the rearward end of the body.

In extremely long or large vehicles, even the water flow over a gas film may form a boundary layer which may become unstable For vehicles where this possibility exists, it is sometimes desirable to provide a number of suction slots similar to slot S3 and S3. spaced in intervals along the axial length of thebody as disclosed in my U.S. Patent No. 3,016,865. Through employment of such suction slots as described above, the boundary layer may be thinned to negligibly small values, and at a location where the gas layer tends to zero, the second of the intake slots S3 is positioned to remove the complete water boundary layer which has been formed and to create a new (essentially boundary layerless) gas-water .interface as described above in connection with the functioning of the structure of FIG. 3. It should also be understood that the apparatus and techniques described above may be used wherever small friction is required with the simultaneous control of pressures. For example, the principles of the present invention may be used in fluid lubricated journal bearings of any type as suggested'in the above-identified patent.

It will, of course, be understood that the torpedo or underwater body 8 shown in the drawing is, in its rearward portion, provided with an essentially double-walled surface, the indicated outer surface 51 being supported and separated from the inner surface 52 by any convenient or suitable supporting means as appears on a greatly exaggerated scale in the diagrammatic section view in FIG. 9. That is to say, it will be understood that the double-wall surface, slots, conduits, pump 25 and gas source 23 shown therein, in fact, occupy a far lesser proportion of the total torpedo volume than would appear from the drawing.

Thus, in FIG. 9, the gas inlet channel S3 may continue between the two members 5]. and 52 and be connected by a conduit 54 to the intake side of any convenient source of gas, such as'the gas source 23. The gas source 23, of course, is also connected by a suitable conduit 53 to the blowing slots S2 on the bottom of the torpedo and, similarly, the suction slots S3 may be connected by a suitable branch conduit 54a to the intake of the pump 25 which may be employed to replenish the compressed air tank 23 in any known manner for recirculation of the gas forming the film over the rearward surface of the torpedo or underwater body 8. Furthermore, as noted above, the water taken in from the channels Wl-W6 is fed through the channel 21,

through the apertures 22 and may be mixed with the propulsion water taken in through the conduit 40 as shown in FIG. 9 and employed for propulsion purposes. It is thus seen that direct contact between the ambient water and the surface of the torpedo exists only with respect to the front or nose portion and the rearward discharge area of the vehicle.

Since an underwater body with an established gas film has a drag which is only a few percent of the drag of a wetted underwater body, a small quantity of water may be all that is required for propulsion. This quantity of water may be taken aboard near .ne axial center of the torpedo at the front end thereof. Water is taken aboard in the front region of the tor edo through the centrally located conduit since this is the only part 1' region or" the vehicle where the vehicle is in contact with -e water, in addition to the rear end of the vehicle. This central induction of propulsion water also has the advantage in that possible stagnation point instabilities are prevented which would effect break-up of the water gas interface.

The distribution of the suction slots depends on the requirements for maintaining an adequate gas thickness which depends in turn on the body configuration. For example, it is possible to design a body which does not require suction slots except near its rear end.

Cross-F low Stability As noted above, gas cross-flow, which occurs from the bottom of the vehicle to the top, is counteracted by a similar flow of gas around the bottom of the vehicle and by removing gas through suction slots at the top of the vehicle such Lat the gas thickness on the bottom and top of the vehicle remain substantially the same. For a gas thickness of about 0.01 inch, these quantities of 'gases, added and removed for control of gas film thick sents the basic problem involved in reducing drag on a submerged vehicle through the use of a lubricating fiuid film.

in order to reduce such cross-flow shear stresses, the underwatebody 3 may, for example, have very small fins or ridges on its surface rearward of the annular slots S1 substantially as shown in FIG. 1. These ridges 5% which are shown greater cross-sectional detail in FIG. 8 may be conveniently extended from a top forward position on the surface to the bottom rearward position of the surface of the torpedo. These fins or ridges are of a height less than the total filrn height and are preferably spaced apart by a distance which is a multiple of their own height.

in FIG. 8 there is shown a fragmentary cross-sectional view on a greatly enlarged scale through the ridges 59, such as those shown, in FIG. 1. These ridges 5b should have a height indicated by the distance i in PEG. 8, which is a fraction of the height L of the gas film. The ridges extend at a relatively small angle with respect to the axis or meridianal direction of the torpedo so that the total gas flow from the bottom to the top oi the torpedo is reduced. As noted above, the ridges are preferably spaced apart a distance which is a multiple of their own height. This spacing, as Well as the height of the ridges, should be calculated and selected to make the total rate of flow of gas from the bottom to the top of the torpedo nearly zero. The design therefore depends on the particular application for which the tor- I pedo is intended, having in mind such factors as intended tice, the necessary apparatus may be far more compactly arranged to allow room for the additional components of conventional nature in the underwater body, such as a torpedo or submarine.

Additionally, by employment of the principles of the present invention, the structural details of apparatus constructed in accordance with the present invention may be simplified by shaping of the underwater body in such a manner that a large number of sucking and blowing slots are not required. The suction and blowing slots are required in order to adjust the thickness of the gas film for two reasons primarily. Thickening of the gas film is required where the gas film is so thin that the shear stress acting from the gas on the water boundary layer exeeds a certain limit so that the Reynolds number of the water boundary layer increases more than is desirable. Removal of the gas is necessary where the thickness of the gas film increases with its inherent disadvantages. Increase in gas film thickness occurs primarily in regions of adverse pressure gradient, i.e., in the range Where the free stream velocity decreases to less than desired values.

By shaping of the underwater body in accordance with the following principles, the requirement for suction and blowing slots over the major portion of the underwater body may be eliminated. If the gas film is sufiiciently thin when introduced around the vehicle, its tendency to grow to uncontrollable thicknesses is reduced in the presence of a favorable gradient. However, under these circumstances, the gas film may be sufiiciently thin to produce an undesirable shear stress acting upon the water. The shear stress, however, may be reduced and effectively rendered negligible by producing in the water surrounding the underwater body, a pressure drop in the direction opposite to the direction of motion of the body. Such a body may be considered a body having continuously accelerated flow over almost its entire length. The acceleration of the velocity in the water near the body must be chosen in such a manner that the shear stress which acts ruin the gas upon the water is essentially Zero. The necessary gradient which is imposed in the water will depend primarily on the viscosity of the gas and the thickness of the gas film.

At the end of the region over which the free streamlines are continuously accelerated in accordance with the principle under discussion, when moving from the front of the torpedo towards the rear thereof, the gas film must, of course, be thinned with a rapidity corresponding to the rapidity, of the pressure increase which is imposed by the water velocity adjacent the body. If this increase of pressure is very rapid, it may be necessary to remove the complete gas layer through one slot located at the rear of the vehicle. In such a case the very end of the underwater body would be in contact with water and would result in some additional friction.

' However, such a design needing only two'slots, namely one in the front which introduces the gas onto the surface of the body, and one at the end of the body which removes the gas, constitutes an unusually simple design.

in accordance with the above disclosed methods, it is possible, by stabilizing the water-gas interface on the body of the torpedo, to reduce the propulsion power required by a factor in the range of 10 to 100 times and, at the same time, to reduce the noise created by the torpedo by more than 1% fold.

It will be understood that modifications and variations be effected by those skilled in the art without departing from the scope of the novel concepts of the present invention, and I wish to embody within the scope of the patent warranted hereon all such embodiments as reasonably and properly come within the scope thereof.

1 claim as my invention:

1. in a body adapted to move submerged relative to a liquid medium, and having drag reduction structure providing an encircling stable gas film about the body,

' said drag reduction structure comprising:

(a) a blunt annular front-end body portion;

so /ease (b) first annularly arranged means, opening on the front of said annular body portion, for withdrawing "a radially outwardly moving liquid-medium boundary-layer; and second annularly arranged means opening on the front of said annular body portion near'the periphery thereof, and closely encircling said first means, for 'flowing the gas film onto the body. 2. In a body adapted to move submerged relative to a liquid medium, and having drag reduction structure providing an encircling stable gas film about the body, said drag reduction structure comprising:

(a) a blunt annular front-end body portion; (b) a plurality of first annularly-arranged radiallyspaced concentric means, each opening on the front of said annular body portion, for withdrawing a radially outwardly moving liquid-medium boundarylayer in radially successive increments; and (c) second annularly arranged means opening on the front of said annular body portion near the periph ery thereof, and closely encircling the outermost of said first means, for flowing the gas film onto the body. 3. In a body adapted to move submerged relative to a liquid medium, and having drag reduction structure providing an encircling stable gas film about the body, said drag reduction structure comprising:

(a) a blunt annular front-end body portion coaxial with the body;

(b) first means defining a first annular channel coaxial with the body and opening on the front of said annular body portion, and adapted to withdraw a radially outwardly moving liquid-medium boundaryiayer; and second annularly arranged means closely encircling said first means, and disposed within said annular front-end body portion, and defining a second channel which opens on the front of said body portion near the periphery thereof, for flowing the gas film onto the body.

4. In a body adapted to move submerged relative to a liquid medium, and having drag reduction structure "providing an encircling stable gas film about the body,

said drag reduction structure comprising:

(a) a blunt annular front-end body portion coaxial with the body;

-(b) a plurality of first annularly-arranged radiallyspaced concentric means defining a plurality of annular channels coaxial with the body and each opening on the front of said annular body portion, and adapted to withdraw a radially outwardly moving liquid-medium boundary-layer in radially successive increments; and t (0) second annularly arranged means opening on the front of said annular body portion near the periphery thereof, and closely encircling the outermost of saidfirst means, for flowing the gas film onto the body.

' 5. In a body adapted to move submerged relative to a liquid medium, and having drag reduction structure providing an encircling stable gas film about the body, said drag reduction structure comprising:

(a) a blunt annular front-end body portion;

(b) annularly arranged means, opening on the front of said annular body portion, for withdrawing a radially outwardly moving liquid-medium boundarylayer;

(6) a pair of radially spaced concentric sleeves jointly defining an axially directed annular opening coaxial with the opening of said withdrawing means, and which opens on the front of said annular body portion near the periphery thereof, said sleeves encircling said withdrawing means; and

(d) a plurality of radially directed members disposed between said sleeves and dividing said annular opening into arplurality of opening segments for jointly flowing the gas onto the body.

6. In a body adapted to move submerged relative to a liquid medium, and having drag reduction structure providing an encircling stable gas film about the body, said drag reduction structure comprising:

(a) a blunt annular front-end body portion;

(b) annularly arranged means, opening on the front of said annular body portion, for withdrawing a radially outwardly moving liquid-medium-boundary-layer;

(c) a pair of radially spaced concentric sleeves jointly defining an axially directed annular opening coaxial with the opening of said withdrawing means, and which opens on the front of said annular body portion near the periphery thereof, said sleeves encircling said withdrawing means;

(d) a plurality of radially directed members disposed between said sleeves and dividing said annular opening into a plurality of opening segments for jointly flowing the gas onto the body;

(e) a plurality of flow passages disposed in one of said sleeves and each connected at one end to one of said opening segments;

(f) a plurality of gas chambers, each chamber being connected to the other end of a plurality of said flow passages; and

(g) means for supplying a gas flow to said chambers 7. In a body adapted to move submerged relative to a liquid medium, and having drag reduction structure providing an encircling stable gas film about the body, said drag reduction structure comprising:

(a) a blunt annular front-end body portion;

(1;) first annularly arranged means, opening on the front of said annular body portion, for withdrawing a radially outwardly moving liquid-medium boundary-layer;

(0) second annularly arranged means opening on the front of said annular body portion near the periphery thereof, and closely encircling said first means, for flowing the gas film onto the body; and

(d) third means defining an axial opening in said annular front-end body portion for receiving a portion of the fluid medium for aiding the relative movement of the body.

8. In a body adapted to move submerged relative to a liquid medium, and having drag reduction structure providing an encircling stable gas film about the body, said drag reduction structure comprising:

(a) a blunt annular front-end body portion;

(b) first annularly arranged means, opening on the front of said annular body portion, for withdrawing a radially outwardly moving liquid-medium boundary-layer;

(c) second annularly arranged means opening on the front of said annular body portion near the periphery thereof, and closely encircling said first means, for flowing the gas film onto the body; and

(d) said annular front-end body portion being centrally externally concave and ported for receiving a portion of the fluid medium for aiding the relative movement of the body.

9. In a method of reducing drag on a body having-a blunt front end and adapted to move submerged relative to a liquid medium, the steps comprising:

(a) incrementally withdrawing in successive annular patterns near the periphery of the blunt front end a boundary layer of the liquid medium formed by contact with the front end of the body; and

(b) flowing a stable laminar gas film radially outwardly from near the outermost of said annular patterns of the blunt front end and thence around a major portion of the body surface.

10. In a method of reducing drag on a body having a blunt front end and adapted to move submerged rela tive to a liquid medium, the steps comprising:

(a) incrementally withdrawing in successive annular patterns near the periphery of the blunt front end 13 a boundary layer of the liquid medium formed by contact with the front end of the body; and

(b) flowing a stable laminar gas film radially outwardly from a series of annularly-arranged forwardly-di rected points near the outermost of said annular patterns of the blunt front end and thence around a major portion of the body surface.

11. In a method of reducing drag on a body having an annular blunt front end and adapted to move submerged relative to a liquid medium, the steps comprising:

(a) withdrawing near the periphery of the blunt front end a boundary layer of the liquid medium formed by contact with the front end of the body;

(b) flowing a stable laminar gas film radially outwardly from the periphery of the blunt front end and thence around a major portion of the body surface; and

(c) withdrawing liquid medium centrally of the annular blunt front end for propulsion purposes.

12. In a method of reducing drag on a body having a blunt front end and adapted to move submerged relative to a liquid medium, the steps comprising:

(a) incrementally withdrawing in successive annular patterns near the periphery of the blunt front end a boundary layer of the liquid medium formed by contact with the front end of the body;

(b) flowing a stable laminar gas film radially outwardly from an annular area where the liquid medium is being accelerated near the periphery of the blunt front end immediately adjacent to the outermost of said annular patterns and thence around a major portion of the body surface; and

(c) withdrawing liquid medium centrally of the annular blunt front end for propulsion purposes.

References Cited in the file of this patent UNITED STATES PATENTS Torazzi Sept. 9, 1919 Casey Mar. 22, 1927 Boerner Sept. 3, 1929 Pearce Aug. 26, 1952 Ouellet Dec. 22, 1953 Giles Jan. 31, 1961 Eichenberger Jan. 16, 1962 FOREIGN PATENTS Great Britain of 1910 Germany Mar. 16, 1921 Great Britain Sept. 9, 1929 France June 28, 1932 France Feb. 2, 1938 Great Britain Oct. 27, 1954 

1. IN A BODY ADAPTED TO MOVE SUBMERGED RELATIVE TO A LIQUID MEDIUM, AND HAVING DRAG REDUCTION STRUCTURE PROVIDING AN ENCIRCLING STABLE GAS FILM ABOUT THE BODY, SAID DRAG REDUCTION STRUCTURE COMPRISING: (A) A BLUNT ANNULAR FRONT-END BODY PORTION; (B) FIRST ANNULARLY ARRANGED MEANS, OPENING ON THE FRONT OF SAID ANNULAR BODY PORTION, FOR WITHDRAWING A RADIALLY OUTWARDLY MOVING LIQUID-MEDIUM BOUNDARY-LAYER; AND (C) SECOND ANNULARLY ARRANGED MEANS OPENING ON THE FRONT OF SAID ANNULAR BODY PORTION NEAR THE PERIPHERY THEREOF, AND CLOSELY ENCIRCLING SAID FIRST MEANS, FOR FLOWING THE GAS FILM ONTO THE BODY. 